1. Technical Field
The present invention relates to an illumination device and a projector.
2. Related Art
In recent years, a light source device utilizing a phosphor is used in a projector (for example, refer to JP-A-2012-108486). In the light source device, excitation light is condensed by a condensing lens onto a phosphor layer, and fluorescence from the phosphor layer is collimated by the condensing lens. In the light source device as described above, the condensing lens not only condenses the excitation light but also collimates the fluorescence. That is, the condensing lens acts not only as a condensing optical system but also as a collimating optical system.
In order to utilize the fluorescence with high efficiency in the projector, the parallelism of the fluorescence emitted from the light source device is required to be high. Moreover, in order to increase the uniformity of an intensity distribution of the fluorescence, the uniformity of an illuminance distribution of the excitation light on the phosphor layer is required to be high. In the related art, however, when the condensing lens is designed so as to uniform the illuminance distribution of the excitation light on the phosphor layer, the parallelism of the fluorescence is reduced due to the influence of chromatic aberration. Conversely, when the condensing lens is designed so as to increase the parallelism of the fluorescence, the uniformity of the illuminance distribution of the excitation light on the phosphor layer is reduced due to the influence of chromatic aberration. In the related art as described above, it is difficult to achieve both the use efficiency of the fluorescence and the uniformity of the intensity distribution of the fluorescence using the optical system that acts not only as a condensing optical system but also as a collimating optical system.